Assembly of a liner and a flange for a vertical furnace as well as the liner and the vertical furnace

ABSTRACT

An assembly of a liner and a flange for a vertical furnace for processing substrates is provided. The liner being configured to extend in the interior of a process tube of the vertical furnace, and the flange is configured to at least partially close a liner opening. The liner comprising a substantially cylindrical wall delimited by the liner opening at a lower end and closed at a higher end and being substantially closed for gases above the liner opening and defining an inner space. The flange comprising: 
     an inlet opening configured to insert and remove a boat configured to carry substrates in the inner space of the liner; 
     a gas inlet to provide a gas to the inner space. The assembly is constructed and arranged with a gas exhaust opening to remove gas from the inner space and a space between the liner and the low pressure tube.

FIELD

The present invention relates to a low pressure vertical furnace and more in particular to an assembly of a liner and a flange for a low pressure vertical furnace and the liner used therein. The liner is configured to extend in the interior of a low pressure process tube of the vertical furnace and the flange configured to partially close an interior of the tube.

BACKGROUND

A vertical processing furnace for processing substrates, e.g., semiconductor wafers may include a heating means, placed around a bell jar-shaped process tube and a substantially cylindrical liner that is coaxially disposed within the process tube. The upper end of the process tube may be closed, for example by a dome-shaped structure, whereas the lower end surface of the process tube may be open.

The liner may be open at its upper end and lower end. The lower end may be partially closed by a flange. An inner space bounded by the liner and the flange forms a process chamber in which wafers to be treated may be processed. Between the liner and the process tube is a circumferential space. The flange may be provided with an inlet opening for inserting a wafer boat carrying wafers into the inner space. The wafer boat may be placed on a door that is vertically moveably arranged and that is configured to close off the inlet opening in the flange.

The flange may further include at least one gas inlet that is in fluidum connection with the inner space bounded by the liner. Additionally, a gas exhaust may be provided that is in fluidum connection with the circumferential space between the liner and the process tube. This gas exhaust may be connected to a vacuum pump for pumping off gas from the circumferential space. This configuration may lead to a gas flow from the gas inlet at the lower end of the liner through the inner space of the liner upwards through the open end of the liner into the circumferential space and to the gas exhaust. The gas in the flow may be a reaction (process) gas for a deposition reaction on the wafers. This reaction gas may also deposit on other surfaces than the wafers within the vertical furnace.

A problem of vertical processing furnaces for processing substrates may be contamination in the inner space of the process tube.

SUMMARY

An improved assembly of a liner and a flange that may cause less contamination may therefore be required.

Accordingly, there is provided an assembly of a liner and a flange according to a first embodiment, the liner being configured to extend in the interior of a low pressure process tube of a vertical furnace. The liner of the assembly may comprise a substantial cylindrical wall delimited by the liner opening at the lower end and a top closure at the higher end. The liner may be substantially closed above the liner opening for gasses and define an inner space. The flange may comprise an inlet opening configured to insert and remove a boat that is configured to carry substrates in the inner space of the liner. The flange may be configured to at least partially close an opening of the tube. The flange may have a gas inlet duct to provide a reaction gas to the inner space. The assembly may be constructed and arranged with a gas exhaust opening to remove gas from the inner space and a space between the liner and the low pressure process tube.

The contamination may be circumvented by closing the liner above the liner opening for reaction gases and removing gas from the inner space and the space between the liner and the process tube by the gas exhaust duct at the flange so that the reaction gases don't reach the space between the liner and the tube. The inside of the process tube and the outside of the liner may therefore be kept clean since substantially no reaction gasses are flowing there.

According to an embodiment there is provided a vertical furnace, comprising:

a low pressure process tube defining an interior;

a heater configured to heat the interior of the tube;

an assembly according to the first embodiment, wherein the flange is partially closing an open end of the process tube leaving a central inlet opening open and wherein the liner extends in the interior of the process tube;

a vertically movably arranged door configured to close off the central inlet opening in the flange and configured to support a wafer boat that is configured to hold substrates.

The vertical furnace has the advantages which have been described above with reference to the assembly of the liner and the flange. An advantage may be that contamination is prevented by providing the liner as a barrier between the inner space and the tube.

According to a further embodiment there may be provided a liner configured to extend in the interior of a low pressure process tube of a vertical furnace comprising:

a substantially cylindrical wall delimited by a liner opening at a lower end and a top closure at a higher end and being substantially closed for gases above the liner opening and defining an inner space wherein the liner comprises silicon carbide.

The various embodiments of the invention may be applied separate from each other or may be combined. Embodiments of the invention will be further elucidated in the detailed description with reference to some examples shown in the figures.

BRIEF DESCRIPTION OF THE FIGURES

It will be appreciated that elements in the figures are illustrated for simplicity and clarity and have not necessarily been drawn to scale. For example, the dimensions of some of the elements in the figures may be exaggerated relative to other elements to help improve understanding of illustrated embodiments of the present disclosure.

FIG. 1 shows a cross-sectional view of a tube of a vertical process furnace including an assembly of a liner and a flange according to an embodiment;

FIG. 2 is a schematic top view of the assembly of FIG. 1;

FIG. 3 is a cross-sectional perspective side view of the assembly over the line from FIG. 2 in which also the process tube of the vertical furnace is shown;

FIG. 4 is a cross-section over the line IV-IV in FIG. 2;

FIG. 5 is a similar cross-section as shown in FIG. 4, but of an embodiment in which the flange is provided with support pads;

FIG. 6 shows a cross-sectional view of a vertical furnace including an assembly of a liner and a flange according to a further embodiment;

FIG. 7 shows a cross-sectional view of a vertical furnace including an assembly of a liner and a flange according to yet a further embodiment;

FIG. 8 depicts a perspective bottom view of an injector according to an embodiment located within the liner according to FIG. 1, 6 or 7; and,

FIG. 9 depicts an injector for use in FIG. 1, 6, 7 or 8.

DETAILED DESCRIPTION

In this application similar or corresponding features are denoted by similar or corresponding reference signs. The description of the various embodiments is not limited to the examples shown in the figures and the reference number used in the detailed description and the claims are not intended to limit what is described to the examples shown in the figures.

FIG. 1 shows a cross-sectional view of a vertical furnace including an assembly of a liner and a flange according to an embodiment. The vertical furnace includes a low pressure process tube 12 defining an interior and a heater H configured to heat the interior.

A liner 2 extends in the interior, the liner comprising a substantially cylindrical wall delimited by a liner opening at a lower end and a dome shape top closure 2 d at the higher end. The liner is substantially closed for gases above the liner opening and defines an inner space I.

A flange 3 may be provided to at least partially close the opening of the low pressure process tube 12. A vertically movably arranged door 14 may be configured to close off a central inlet opening O in the flange 3 and may be configured to support a wafer boat B that is configured to hold substrates W. The flange 3 may be partially closing an open end of the process tube 12. The door 14 may be provided with a pedestal R. The pedestal R may be rotated to have the wafer boat B in the inner space rotating. Under the lowest substrate in the boat B a flow space may be provided to prevent the flow of reaction gas between the substrates W in the boat.

In the example shown in FIG. 1, the assembly 1 comprises a liner 2 comprising a substantial cylindrical liner wall having an outer substantial cylindrical surface 2 a and an inner substantial cylindrical surface 2 b. The flange 3 is configured to at least partially close the tube opening and the liner opening defined more precisely by the lower end surface 2 c of the liner 2. The flange 3 comprises:

an inlet opening O configured to insert and remove the boat B configured to carry substrates W in the inner space I of the liner 2;

a gas inlet 16 to provide a gas F, for example a reaction gas to the inner space I; and,

a gas exhaust duct 7 to remove gas from the inner space.

The gas inlet 16 may be provided with an injector 17 constructed and arranged within the assembly to extend vertically into the inner space I along the substantial cylindrical wall of the liner 2 towards the higher end and comprising an injector opening 18 to inject gas in the inner space I.

Gas exhaust openings 8 connected to the gas exhaust duct 7 for removing gas from the inner space may be constructed and arranged below the injector opening 18. In this way, by closing the liner 2 above the liner opening for gases, providing a gas to the inner space with the injector 17 through the injector opening 18 at an upper end of the inner space I and removing gas from the inner space by the gas exhaust openings 8 at a lower end of the inner space a down flow F in the inner space of the liner 2 may be created. This down flow F may transport contamination of reaction byproducts, particles from the substrate W, the boat B, the liner 2 and/or the support flange 3 downward to the exhaust openings 8 away from the processed substrates W.

The gas exhaust opening 8 for removing gas from the inner space I may be provided below the open end of the liner 2. This may be beneficial since a source of contamination of the process chamber may be formed by the contact between the liner 2 and the flange 3. More specifically the source may exist, at the position where a lower end surface of the liner at the open end is in contact with the flange. During the processing of substrates, and in particular during unloading of a boat after processing, the liner and the flange may be subjected to heat that increases the temperature of both liner and flange. Due to the temperature increase, liner and flange may experience thermal expansion, which causes them to radially expand. As the liner and the flange may have different coefficients of thermal expansion, because for example the liner 2 may be made from silicon carbide and the flange from metal, the liner and the flange may move with respect to each other during expansion. This may cause friction between the lower end surface of the liner and the upper surface of the flange, which may result in contaminants, e.g., small particles breaking away from liner and/or flange. The particles may migrate into the process chamber and may contaminate the process chamber and the substrates which are being processed.

By closing the liner above the liner opening for gases, providing a process gas to the inner space with the gas injector at an upper end of the inner space and removing gas from the inner space by the gas exhaust at a lower end of the inner space, a down flow in the inner space may be created. This down flow may transport the particles from the liner-flange interface downward to the exhaust away from the processed substrates.

The gas exhaust openings 8 may be constructed and arranged in the flange 3 between the liner 2 and the tube 12 for removing gas from the circumferential space between the liner 2 and the tube 12. In this way the pressure in the circumferential space and the interior space I may be made equal and in a low pressure vertical furnace may be made lower than the surrounding atmospheric pressure surrounding the tube 12. The vertical furnace may be provided with a pressure control system to remove gas from the interior of the tube (including the inner space of the liner) of the low pressure vertical furnace.

In this way the liner 2 may be made rather thin and of a relatively weak material since it doesn't have to compensate for atmospheric pressure. This creates a larger freedom in choosing the material for the liner 2. The thermal expansion of the material of liner 2 may be chosen such that it may be comparable with the material deposited on the substrate in the inner space. The latter having the advantage that the expansion of the liner and the material deposited also on the liner may be the same. The latter minimizes the risk of the deposited material dropping of as a result of temperature changes of the liner 2.

The tube 12 may be made rather thick and of a relatively strong compressive strength material since it may have to compensate for atmospheric pressure with respect to the low pressure on the inside of the tube. For example, the low pressure process tube 12 can be made of 5 to 8, preferably around 6 mm thick Quartz. Quartz has a very low Coefficient of Thermal Expansion (CTE) of 0.59×10-6 K-1 (see table 1) which makes it more easy to cope with thermal fluctuations in the apparatus. Although the CTE of the deposited materials may be higher (e.g., CTE of Si3N4=3×10-6 K-1, CTE of Si=2.3×10-6 K-1) the differences may be relatively small. When films are deposited onto tube made of quartz, they may adhere even when the tube goes through many large thermal cycles however the risk of contamination may be increasing.

The liner 2 may circumvent any deposition on the inside of the tube 2 and therefore the risk of deposition on the tube 12 dropping off may be alleviated. The tube may therefore be made from Quartz.

A liner 2 of silicon carbide (CTE of SiC=4×10-6 K-1) may provide an even better match in CTE between deposited film and liner, resulting in a greater cumulative thickness before removal of the deposited film from the liner may be required. Mismatches in CTE result in cracking of the deposited film and flaking off, and correspondingly high particle counts, which is undesirable and may be alleviated by using a SIC liner 2. The same mechanism may work for the injector 17 however for injectors 17 it may be the case that the injector may be breaking if too much material with different thermal expansion is deposited. It may therefore be advantageously to manufacture the injector 17 from silicon carbide or silicon.

TABLE 1 Coefficient of Thermal Expansion (CTE) of Materials in Semiconductor Processing Material Thermal expansion (ppm/K) Quartz 0.59 Silicon nitride 3 Silicon 2.3 Silicon carbide 4.0 Tungsten 4.5

Whether a material is suitable for the liner 2 and or the injector 17 may be dependent on the material that is deposited. It is therefore advantageously to be able to use material with substantially the same thermal expansion for the deposited material as for the liner 2 and/or the injector 17. It may therefore be advantageously to be able to use material with a thermal expansion for the liner 2 and/or the injector 17 relatively higher than that of quartz. For example Silicon Carbide SiC may be used. The silicon carbide liner may be between 4 to 6, preferably 5 mm thick since it doesn't have to compensate for atmospheric pressure. Pressure compensation may be done with the tube.

For systems depositing metal and metal compound materials with a CTE between about 4×10-6 K-1 and 6×10-6 K-1, such as TaN, HfO2 and TaO5, the liner and injector materials preferably may have a CTE between about 4×10-6 K-1 and 9×10-6 K-1, including, e.g., silicon carbide.

For deposition of material with even a higher CTE, the liner and/or injector materials may be chosen as for example depicted by table 2.

TABLE 2 Coefficient of Thermal Expansion (CTE) of Ceramic Construction Materials Material Thermal expansion (ppm/K) Macor 12.6 Boron Nitride 11.9 Glass, ordinary 9 Mullite 5.4

The assembly may be provided with a purge gas inlet 19 mounted on the flange for providing a purge gas P to the circumferential space S between an outer surface of the liner 2 b and the process tube 12. The purge gas inlet comprises a purge gas injector 20 extending vertically along the outer surface of the cylindrical wall of the liner 2 from the flange 3 towards the top end of the liner. The purge gas P to the circumferential space S may create a flow in the gas exhaust openings 8 and counteract diffusion of reaction gas from the exhaust tube 7 to the circumferential space S.

The flange 3 may have an upper surface. The liner 2 may be supported by support members 4 that may be connected to the outer cylindrical surface of the liner wall 2 a and each have a downwardly directed supporting surface. The liner may also be supported directly on the upper surface of the flange 3 with it lower surface 2 c.

The supporting surfaces of the support members 4 may be positioned radially outwardly from the inner cylindrical surface 2 b of the liner 2. In this example, the supporting surfaces of the supporting members 4 may be also positioned radially outwardly from the outer cylindrical surface 2 a of the liner 2 to which they are attached. The downwardly directed supporting surface of the support members 4 may be in contact with the upper surface of the flange 3 and support the liner 2.

The support flange 3 of the closure may include gas exhaust openings 8 to remove gas from the inner space of the liner 2 and the circular spaces between the liner 2 and the low pressure tube 12. At least some of the gas exhaust openings may be provided in the upper surface of the flange 3 radially outside of the liner 2. At least some of the gas exhaust openings may be provided near the liner opening. The gas exhaust openings 8 may be in fluid connection with a pump via exhaust duct 7 for withdrawing gas from the inner space and the circumferential space between the process tube 12 and the liner 2. Any particles, which may be created by friction between the support members 4 and the upper surface part of the support flange 3 may be drained along with the gas through the gas exhaust openings 8. In any case, the released particles will not be able to enter the process chamber around the substrates W.

FIG. 2 is a schematic top view of the assembly of FIG. 1. The figure shows the liner 2 with the cylindrical wall defining an inner substantially cylindrical surface 2 b and an outer substantially cylindrical surface 2 a that form an opening 13 for inserting a boat configured to carry substrates.

Also visible are the support members 4. In this example, the liner 2 has three support members 4 that are equally spaced along the circumference of the outer cylindrical surface 2 a of the liner 2. The support members 4 may be embodied as notches that are connected to the outer cylindrical surface 2 a of the cylindrical wall of the liner 2. The flange may be provided with positioning projections 5 that extend upwards from the upper surface 3 a of the flange. The positioning projections 5 may engage the support members 4 on a tangential end surface thereof. As a result, the positioning projections 5 have a centering function for the liner 2 relative to the support flange 3. The positioning projections 5 are spatially separated from the outer cylindrical surface 2 a of the liner 2 allowing the liner 2 to radially expand.

The liner 2 and the notches forming the support members 4 may be manufactured from quartz, silicon or silicon carbide. Instead of three support members 4, alternative embodiments may include two support members 4 or more than three support members 4. Furthermore, the support members 4 are spaced radially outwardly from the inner cylindrical surface 2 b and, preferably, also radially outwardly from the outer cylindrical surface 2 a of the liner 2. Also clearly illustrated is the space between the outer cylindrical surface 2 a of the liner 2 and the positioning projections 5 so that radial expansion of the cylindrical liner wall 2 is possible. The tangential length of the supporting members 4 may typically be in the range of 1-5 cm. The liner 2 delimiting the inner space may have a radially outwardly extending bulge 2 e to accommodate the injector 17 or a temperature measurement system in the inner space.

FIG. 3 is a partial perspective cross-sectional view over the line in FIG. 2 in which also the process tube 12 of the vertical process furnace is shown. The flange may be provided with a groove 15 constructed and arranged for providing a seal such as an O-ring therein to provide for a good sealing between the flange 3 and the tube 12. This good sealing is necessary because the flange 3, tube 12 and the O-ring may form part of the pressure barrier between the outside atmospheric pressure and the low pressure inside the tube 12. The O-ring may be provided at the interface of the quartz because quartz has relatively low thermal expansion so there is not much movement of the quartz with respect to the O-ring which may cause wear of the O-ring.

FIG. 3 further shows the liner 2 with a support member 4, which is attached to the outer cylindrical surface 2 a of the liner 2. Clearly visible is that the support member 4 may be positioned radially outwardly with regard to the cylindrical wall of the liner 2. The downwardly directed supporting surface of the support member 4 may be in contact with the upper surface 3 a of the flange 3 and may support the liner 2. Also visible is that the flange 3 may have a first upper surface part 3 a _(l), which extends under the support member 4 and a second upper surface part 3 a ₂, which may extend under the lower end surface 2 c of the cylindrical wall of the liner 2. In this example the second upper surface part 3 a ₂ may be formed as a circular groove, with an inner diameter smaller than the inner diameter of the liner 2. The outer diameter of the groove that forms the second upper surface part 3 a ₂ may have an outer diameter that is larger than the outer diameter of the liner 2.

The support member 4 may support the liner 2 on the first upper surface part 3 a ₁ so that the lower end surface 2 c of the liner 2 is vertically spaced apart from the second upper surface part 3 a ₂ of the flange 3. Thus a gap may be formed between the lower end surface 2 c of the liner 2 and the second upper surface part 3 a ₂ of the support flange 3. By virtue of this gap, there may be no contact between the liner 2 and the upper surface of the flange 3 adjacent the inner cylindrical surface 2 b of the liner wall 2. That there is no contact between the liner 2 and the upper surface of the flange 3 adjacent the inner cylindrical surface 2 b may reduce the risk of any particles, which may be created by friction between the liner 2 and the upper surface 3 a. The gap may be between 0.1 to 10, preferably 0.2 and 0.5 mm. The support member 4 additionally may include a recess 10 that extends along the tangential length of the support member 4 and has a downwardly directed side that is open.

FIG. 4 is a cross-section over the line Iv-Iv in FIG. 2. The radially inward recess edge 10 a may be located radially outwardly relative to the inner cylindrical surface 2 b of the liner 2. The radially outward recess edge 10 b of the recess 10 may be positioned radially inward with regard to the supporting surface of the support member 4. As a result, the recess 10 may be positioned at least partially across the circular groove 3 a ₂ in the support flange 3; the radially inward recess edge 10 a may be located radially inward of groove 3 a ₂ outer diameter and the radially outward recess edge 10 b may be located radially outward of groove 3 a ₂ outer diameter. This configuration may allow a flow of reaction gas to flow from the space delimited by the inner cylindrical surface 2 b to the space delimited by the outside of the outer cylindrical surface 2 a of the liner 2 and a process tube 12 (which is illustrated in FIG. 3).

Any particles that may be created by the friction between the downwardly directed surface of the support member 4 and the upper surface 3 a _(i) of the support flange 3 that is opposite the support member 4, may be transported away from the gap between the lower end surface 2 c and the upper surface 3 a of the flange. The gas including the particles may be removed through the gas exhaust openings 8 and subsequently exhaust duct 7 towards a pump.

FIG. 5 is similar a cross-section over the line IV-IV in FIG. 2 of a different embodiment in which the support flange 3 may be provided with a support pad 11. FIG. 5 depicts the liner 2, support member 4 and the support flange 3. The support flange 3 in this example may be provided with a support pad 11 that is embedded in the support flange 3. The support pad 11 may be in contact with the downwardly directed supporting surface of the support member 4 and may be configured to reduce the friction between the support flange 3 and the supporting surface of the support member 4. In order to provide said reduction of friction, the support pad 11 may be made of a material with a relatively low constant of friction, such as for example Teflon, Polyimide, PEEK, Hastelloy or any other suitable material. In addition, the support pad 11 may also be made of a metal having a coating of a material with a relatively low constant of friction, such as for example Teflon, Polyimide, PEEK, Hastelloy, other polymeric coatings or a coating of a diamond-like carbon.

FIGS. 6 and 7 show a cross-sectional view of a vertical process furnace including an assembly of a liner 2 and a flange 3 according to further embodiments. FIG. 6 is a cross sectional side view of an example of a vertical process furnace, including a low pressure process tube 12 defining a low pressure interior process tube space, a heater configured to heat the interior process tube space, a vertically movable door configured to close off the central inlet opening in the flange 3 and configured to support a wafer boat B that is configured to hold substrates; and wherein the flange 3 is partially closing an open end of the process tube 12 and wherein the liner 2 extends in the interior process tube space. The door may be provided with a rotator M to rotate the wafer boat B in the inner space. In between the rotator M and the wafer boat B a pedestal R may be provided. The pedestal R may be provided with heaters and/or thermal insulators to improve the heat uniformity for the wafers in the boat B.

The liner 2 may be closed at a higher end for example with a dome shape and may be substantially closed for gases above the liner opening. The flange 3 comprises an inlet opening configured to insert and remove a boat B configured to carry substrates in the inner space of the liner 2. The gas inlet 16 may comprise an injector 17 constructed and arranged within the assembly to extend into the inner space along the cylindrical wall of the liner 2 towards the higher end. The injector 17 in FIG. 6 may be provided with multiple holes provided along the length of the injector 17 to inject gas in the inner space.

The injector 17 in FIG. 7 may be provided with one big opening near the top end of the injector to inject gas in the inner space. The injector 17 of FIG. 7 with one big opening at the end of the injector may also be combined with one or more injectors according to FIG. 6 with multiple holes along the length in this way each part of the inner space may be provided with gas. The liner 2 delimiting the inner space may have a radially outwardly extending bulge to accommodate the injector 17.

The gas exhaust opening 8 for removing gas may be constructed and arranged at a lower end of the inner space I. In this way by closing the liner 2 above the liner opening for gases, providing a process gas to the inner space with the gas injector 17 and removing gas from the inner space I by the gas exhaust opening 8 at a lower end of the inner space, a down flow in the inner space I of the liner 2 may be created. This down flow may transport contamination of reaction byproducts, particles from the substrates, the boat B, the liner 2 and/or the support area of the liner 2 on the flange 3 downward and radially outward to the exhaust 8 away from the processed substrates W. The gas exhaust 8 for removing gas from the inner space I may be provided below the open end of the liner 2.

The assembly may be provided with a temperature measurement system 22 mounted on the flange 3 and extending along an outer surface of the cylindrical wall of the liner 2 towards the top end of the liner to measure a temperature. The temperature measurement system 22 may comprise a beam with a plurality of temperature sensors provided along the length of the beam to measure the temperature at different heights along the liner 2. Since the temperature measurement system 22 is positioned outside the liner 2 deposition may not reach the temperature measurement system 22. This may be beneficial because the deposition may disturb the temperature measurement. Further the temperature measurement system 22 may comprise quartz and therefore have a different expansion coefficient than the deposited material causing a risk of particles and breaking of the temperature measurement system 22. The liner 2 may be provided with an radially inwardly extending bulge to accommodate the temperature measurement system.

A purge gas inlet may be provided at a bottom of a circumferential space S between the liner 2 and the tube 12 to provide a purge gas P between the liner 2 and the tube 12. The assembly may be constructed and arranged such that there is a narrow gap 21 between a lower surface of the liner 2 and the upper surface of the flange 3. The purge gas may flow through the narrow gap between the liner 2 and the flange 3 towards the exhaust opening 8 and may create a counter flow. The gap may be 0.1 to 10 mm, preferably between 0.2 and 0.5 mm. The counter flow may circumvent that the process gas from the injector 17 diffuses through the gap into the circumferential space. The circumferential space S may therefore not be contaminated by the process gas.

The assembly may be provided with a purge gas injector 20 mounted on the flange 3 for providing a purge gas to the circumferential space between an outer surface of the liner 2 and an inner surface of the processing tube 12 such as depicted in FIG. 7. The purge gas injector 20 may be extending along the outer surface of the cylindrical wall of the liner 2 from the flange 3 towards the top end of the liner. In this way it may be easier to get the right purge gas flow over the whole circumference of the circumferential space with only one purge gas injector 20.

A vertical furnace according to an embodiment may comprise:

a low pressure process tube defining an interior;

a heater configured to heat the interior of the tube;

a flange partially closing an open end of the process tube leaving a central inlet opening open and an injector constructed and arranged within the assembly to extend into the interior towards a higher end of the tube and comprising at least one opening to inject gas. A pattern of openings extending in the vertical direction may be provided along the injector. A horizontal, inner cross-section of a gas conduction channel inside the injector may be between 100 and 1500, preferably between 200 and 1000, and most preferably between 300 and 500 mm².

The horizontal, inner cross-section of the gas conduction channel inside the injector may have a shape with a dimension in a direction tangential to the circumference of the substantially cylindrical tube which may be larger than a dimension in a radial direction.

The diameter of the openings may be between 1 to 15 mm, preferably between 3 to 12 mm, more preferably between 4 and 10 mm. The area of the openings may be between 1 to 200 mm², preferably between 7 to 100 mm², more preferably between 13 and 80 mm².

The vertical distance between the openings may decrease when going from the lower end to the top end of the injector. The number of openings may be between 2 and 40, preferably 3 and 30, and more preferably 4 and 10.

The openings may be configured such that gas is injected in at least two different directions. The opening may have a concave shape from the inside to the outside of the injector. The openings may be positioned on two vertically extending, spaced apart branches of the injector. The injector may have one opening near the top end of the tube.

An assembly of a liner and a flange may be provided. The liner may be configured to extend in the interior of the low pressure tube of the vertical furnace. The liner may comprise a substantially cylindrical wall delimited by a liner opening at a lower end and a top closure at a higher end and being substantially closed for gases above the liner opening and defining an inner space. The flange may be configured to at least partially close an opening of the tube and comprise:

an inlet opening configured to insert and remove a boat configured to carry substrates in the inner space of the liner; and

a gas inlet to provide a gas to the inner space. The assembly may be constructed and arranged with a gas exhaust opening to remove gas from the inner space and a space between the liner and the low pressure tube.

FIG. 8 depicts a perspective bottom view on an injector located within the liner 2. The injector 17 may comprise multiple injector branches, for example two injector branches 22, and 23, each provided with a separate gas feed conduit connection 24 and 25 respectively. Branch 22 injects gas into the lower part of the inner space and branch 23 injects gas into the upper part of the inner space. The branches may be connected by connecting parts. Additional injector branches may be provided, for example one with a single opening near the end of the liner. However, it is not essential for the invention that the injector comprises two or more injector branches.

The injector may be provided with a pattern of openings 26, the pattern extending substantially over the wafer load. According to the invention the total cross section of the openings is relatively large, for example between 100 and 600, preferably between 200 and 400 mm². And the inner cross-section of the injector 17, available for the conduction of source gas, may be between 100 and 600, preferably 200 and 500 mm² or more.

The opening diameter may be between 1 to 15 mm, preferably between 3 to 12 mm, more preferably between 4 and 10 mm. The area of the opening may be between 1 to 200 mm², preferably between 7 to 100 mm², more preferably between 13 and 80 mm². Larger openings may have the advantage that it takes longer for the openings to clog because of deposited layers within the openings.

In the example shown in FIG. 8, the injector as a whole comprises 40 openings. For a diameter of 3 mm, the total cross-section of the openings may be 40×3×3×π/4=282 mm². The cross-section of each of the branches of the injector is about 11×30=330 mm². Other injectors may have 20 openings with a 4 mm diameter giving a total area of 251 mm². Other injectors may have 5 openings with a 8 mm diameter giving a total area of also 251 mm².

In each injector branch 22, 23, the openings may be provided pair-wise, at the same height, the two openings may inject the gas in two directions, under an angle of about 90 degrees, to improve the radial uniformity.

The openings may be positioned on the injector in a vertically and horizontally spaced apart relationship. The opening pattern on one injector branch may extend vertically with a higher concentration of openings at the higher part of the branch to compensate for a reducing gas flow in the higher part. The injector branches may be injector tubes, each injector tube with its feed end connected to a separate gas supply conduit. The injector tube may be connected via a separate gas supply conduit to a separate gas source for the separate injection of two or more source gases. The opening pattern on one injector branch may extend vertically over only a part of the boat. The injector 17 may be accommodated in bulge 2 e in the liner 20.

The assembly may be provided with a temperature measurement system mounted on the flange and extending along an inner or outer surface of the cylindrical wall of the liner 2 towards the top end of the liner to measure a temperature. The temperature measurement system may comprise a beam with a plurality of temperature sensors provided along the length of the beam to measure the temperature at different heights along the liner.

A second bulge 2 f may be provided in the liner 2 to accommodate the beam with the plurality of temperature sensors for measurement of the temperature inside the inner space if configured along an inner surface of the liner. As depicted the bulge is extending outwardly so as to accommodate the temperature measurement system on the inside of the liner however the bulge may also be extending inwardly to accommodate the temperature measurement system on the outside of the liner. By accommodating the injector and the temperature system in the bulges 2 e and 2 f respectively, the inner space can be kept substantially cylindrical symmetric, which is advantageous for the uniformity of a deposition process. Process tube 12 may be provided at the bottom end with a broadening flange 27.

FIG. 9 depicts an injector 17 for use in the assembly of FIG. 1, 6, 7 or 8. Five injector openings 18 are provided in the injector 17 numbered 31, 33, 35, 37, 39 from the top downward. The distance between the openings near the top of the injector 17 may be reduced compared to the distance at a lower end of the injector 17 to compensate for a reduced pressure at the top of the injector. The distance between the first and second openings 31, 33 may be between 45 and 49, preferably 47 mm, between openings 33 and 35 it may be between 51 and 55, preferably 53 mm, between opening 35 and 37 it may be between 55 and 59, preferably 57 mm, and between 37 and 39 it may be between 70 and 100, preferably 81 mm to compensate for the pressure reduction.

The total cross-section of the openings may be relatively large so that the pressure inside the injector is kept at a relatively low value. The diameter of the openings 18 may be between 4 and 15 mm. For example the openings may have a diameter of 8 mm. Deposition within the openings of the injector may cause clogging of the injector openings. By having larger openings, e.g., 4 to 15 mm, preferably 8 mm it takes a longer time for the injector openings to clog up, which is increasing the life time of the injector.

The horizontal, inner cross-section of a gas conduction channel inside the injector may have an oblong shape with a dimension in a direction tangential to the circumference of the substantially cylindrical liner which is larger than a dimension in a radial direction. The lower part 28 of the injector 17 may have a smaller cross-section and accordingly a higher pressure. Normally this may cause extra deposition but since the temperature may be lower in this part the deposition rate may still be acceptable.

The opening 18 of the gas injector 17 may be configured to reduce clogging of the opening. The opening may have a concave shape from the inside to the outside. The concave shape with the surface area of the opening on a surface on the inside of the injector larger than the surface area of the opening 18 on the outside of the injector may reduce clogging. The larger area on the inside allows more deposition at the inner side where the pressure and therefore the deposition is larger. On the outside the pressure is reduced and therefore the deposition is also slower and a smaller area may collect the same deposition as a larger diameter on the inside.

Reducing the pressure with the injector may result in a reduction of the reaction rate within the injector 17 because the reaction rate typically increases with increasing pressure. An additional advantage of a low pressure inside the injector is that gas volume through the injector expands at low pressure and for a constant flow of source gas the residence time of the source gas inside the injector reduces correspondingly. Because of the combination of both, the decomposition of the source gases can be reduced and thereby deposition within the injector may be reduced as well.

Deposition within the injector may cause tensile strength in the injector causing the injector to break when temperature is changing. Less deposition within the injector therefore prolongs the life time of the injector 17. The injector may be made from a material which has the coefficient of thermal expansion of the material deposited with the process gas. For example, the gas injector may be made from silicon nitride if silicon nitride is deposited or from silicon if silicon is deposited by the process gas. The thermal expansion of the deposited layer within the injector may therefore match the thermal expansion of the injector, decreasing the chance that the gas injector may break during changes of temperature. Silicon carbide may be a suitable material for the injector 17 because it has a thermal expansion which may match many deposited materials

A disadvantage of a low pressure inside the injector is that the conduction of the injector decreases significantly. This would lead to a poor distribution of the flow of source gas over the opening pattern over the length of the injector: the majority of source gas will flow out of the holes near the inlet end of the injector. To facilitate the flow of source gas inside the injector, along the length direction of the injector, the injector may be provided with a large inner cross section. In order to be able to accommodate the injector according to the invention inside the reaction space, the tangential size of the injector may be larger than the radial size and the liner delimiting the reaction space may be provided with an outwardly extending bulge to accommodate the injector.

In the preferred embodiment the two source gases, providing the two constituting elements of the binary film, are mixed in the gas supply system prior to entering the injector. This is the easiest way to ensure a homogeneous composition of the injected gas over the length of the boat. However, this is not essential. Alternatively, the two different source gases can be injected via separate injectors and mixed after injection in the reaction space.

The use of two injector branches allows some tuning possibilities. When gas of substantially the same composition is supplied to both parts of the injector, via separate source gas supply, the flows supplied to the different injector branches can be chosen different to fine-tune the uniformity in deposition rate over the boat. It is also possible to supply gas of different composition to the two lines of the injector to fine-tune the composition of the binary film over the boat. However, the best results may be achieved when the composition of the injected gas was the same for both injector lines.

While specific embodiments have been described above, it will be appreciated that the invention may be practiced otherwise than as described. The descriptions above are intended to be illustrative, not limiting. Thus, it will be apparent to one skilled in the art that modifications may be made to the invention as described in the foregoing without departing from the scope of the claims set out below. Various embodiments may be applied in combination or may be applied independently from one another. 

1. An assembly of a liner and a flange, the liner being configured to extend in the interior of a low pressure tube of a vertical furnace, the liner comprising: a substantially cylindrical wall delimited by a liner opening at a lower end and a top closure at a higher end and being substantially closed for gases above the liner opening and defining an inner space, the flange being configured to at least partially close an opening of the low pressure tube and comprising: an inlet opening configured to insert and remove a boat configured to carry substrates in the inner space of the liner; and a gas inlet to provide a gas to the inner space, wherein the assembly is constructed and arranged with a gas exhaust duct to remove gas from the inner space and a space between the liner and the low pressure tube through a gas exhaust opening in the flange.
 2. The assembly according to claim 1, wherein the gas inlet comprises an injector, constructed and arranged within the assembly to extend into the inner space along the substantially cylindrical wall of the liner towards the higher end and comprising at least one opening to inject gas in the inner space.
 3. The assembly according to claim 2, wherein a pattern of openings extending in the vertical direction is provided along the injector.
 4. The assembly according to claim 2, wherein the horizontal, inner cross-section area of a gas conduction channel inside the injector is between 100 and 1500 mm².
 5. The assembly according to claim 2, wherein the horizontal, inner cross-section of a gas conduction channel inside the injector has a shape with a dimension in a direction tangential to the circumference of the substantially cylindrical liner which is larger than a dimension in a radial direction.
 6. The assembly according to claim 2, wherein the area of the at least one opening may be between 1 to 200 mm².
 7. The assembly according to claim 3, wherein the vertical distance between the openings decreases when going from the lower end to the top end of the injector.
 8. The assembly according to claim 3, wherein the openings are configured such that gas is injected in at least two different directions.
 9. The assembly according to claim 2, wherein the at least one opening has a concave shape from the inside to the outside.
 10. The assembly according to claim 2, wherein the openings are positioned on two vertically extending, spaced apart branches of the injector.
 11. The assembly according to claim 2, wherein the injector comprises one openings near the top end of the liner.
 12. The assembly according to claim 1, wherein the liner delimiting the inner space has a radially outwardly extending bulge.
 13. The assembly according to claim 1, wherein the gas exhaust opening for removing gas from the inner space is provided below the open end of the liner.
 14. The assembly according to claim 1, wherein the assembly is provided with a purge gas inlet mounted on the flange for providing a purge gas to the space between the liner and the low pressure tube.
 15. The assembly according to claim 14, wherein the purge gas inlet comprises a purge gas injector extending along the outer surface of the substantially cylindrical wall of the liner towards the top end of the liner.
 16. The assembly according to claim 1, wherein the assembly is provided with a temperature measurement system mounted on the flange and extending along the substantially cylindrical wall of the liner towards the top end of the liner to measure a temperature.
 17. The assembly according to claim 16, wherein the temperature measurement system is arranged along an outer surface of the liner.
 18. The assembly according to claim 17, wherein the liner is provided with an radially inwardly extending bulge to accommodate the temperature measurement system.
 19. The assembly according to claim 1, wherein at least one of the liner and the gas injector comprises a material selected from silicon carbide and silicon.
 20. The assembly according to claim 1, wherein the assembly is configured and arranged such that there is a gap between a lower surface of the liner and the upper surface of the flange.
 21. The assembly according to claim 1, wherein the upper surface of the flange is provided with a groove for accommodating seal to seal the low pressure tube.
 22. The assembly according to claim 1, wherein the exhaust opening is disposed in an area that is positioned radially outside the outer substantially cylindrical surface of the liner wall.
 23. A vertical furnace comprising: a heater configured to heat the interior of the low pressure tube; an assembly according to claim 1; and a vertically movably arranged door configured to close off the central inlet opening in the flange and configured to support a wafer boat that is configured to hold substrates.
 24. The vertical furnace according to claim 23, wherein the door is provided with a rotator to rotate the wafer boat in the inner space.
 25. The vertical furnace according to claim 23, wherein a seal is provided between the upper surface of the flange and the low pressure tube to seal the low pressure tube.
 26. The vertical furnace according to claim 23, wherein a pressure control system is provided to remove gas from the interior of the low pressure tube via the gas exhaust opening.
 27. The vertical furnace according to claim 23, wherein the low pressure tube is constructed and arranged to provide a pressure barrier between a low pressure interior space of the low pressure tube, comprising the inner space and the liner, and the atmospheric pressure space outside the low pressure tube.
 28. A liner being configured to extend in the interior of a low pressure tube of a vertical furnace comprising: a substantially cylindrical wall delimited by a liner opening at a lower end and a top closure at a higher end and being substantially closed for gases above the liner opening and defining an inner space, wherein the liner comprises silicon carbide.
 29. The liner according to claim 28, wherein the silicon carbide liner is between 4 to 6 mm thick. 